This invention relates generally in injection lasers and, more particularly, to heterostructure injection lasers having multi-emission capability.
Higher power outputs are being sought in semiconductor junction lasers to meet requirements necessary for optical fiber transmission, optical disk writing and integrated optical components and circuits. To achieve higher output powers from injection lasers, a wide contact stripe region has been proposed wherein stripe widths in excess of, for example, 20 .mu.m, were employed in conventionally known double heterojunction and single heterojunction injection lasers. The width of the stripe was increased to spread the current density over a larger region of the light guiding layer of the device thereby spreading out the developed power by virtue of the larger emitting area. This also reduced the potential of structural damage and degradation of the laser device due to higher current and power densities established where narrower stripe geometries are employed.
Injection lasers have been known to have a stripe width of approximately 75 .mu.m, achieving pulsed output powers of approximately 650 mW.
A disadvantage of these wide stripe lasers has been that transverse mode operation along the p-n junction plane is not stable. On one hand these broad stripe lasers operate in one or more higher order transverse modes exhibiting a broad divergence in the far field radiation pattern, which pattern may fluctuate with time or with driving current. On the other hand, multiple filaments may be simultaneously established in the pumped regions of the light guiding active layer resulting in uncontrolled optical interference fringes in the laser beam.
Greater power outputs have been realized where more than one contact stripe may be employed on the same laser device and if their stripe separation is small enough, optical coupling can be achieved due to transverse optical wave overlapping. This is disclosed in U.S. Pat. No. 3,701,044 and in Applied Physics Letters, Volume 17, Number 9, pages 371-373. With such overlapping, the two established lasers, upon pumping, operate in a phase-locked state. However, as indicated in these disclosures, several transverse modes were present so that stable beam output was not achieved.
It has already been known that with very narrow stripe geometry, such as 2 .mu.m wide, lowest order or fundamental transverse mode can be achieved at least at current pumping levels near threshold. See Japanese Journal of Applied Physics, Volume 16, Number 4, April, 1977, pages 601-607. While such narrower stripe geometry may be used in a multistripe configuration, higher order transverse modes may appear at higher current levels and a variable range of beam divergence occurs in the far field pattern over a wide range of pumping currents.